The present relates to a method and system for multisource intruder correlation and, more particularly to a method and system for intruder/target correlation between a Global Positioning System (GPS) based air traffic control system, such as Automatic Dependent Surveillance Broadcast (ADS-B), and Traffic Alert and Collision Avoidance System (TCAS) intruder in an air traffic control environment.
The recent advent of the use of Automatic Dependent Surveillance-Broadcast (ADS-B), an advanced air ground traffic control system, has facilitated the integration of this system with the pre-existing Traffic Alert and Collision Avoidance System (TCAS).
ADS-B is a technology which allows aircraft to broadcast information such as identification, position, altitude. This broadcast information may be directly received and processed by other aircraft or received and processed by ground systems for use in improved situational awareness, conflict avoidance and airspace management. ADS-B incorporates the use of Global Positioning System (GPS) or other similar navigation systems as a source of position data. By using GPS or the like, ADS-B has the capacity to greatly improve the efficiency and safety of the National Airspace System.
ADS-B provides for an automatic and periodic transmission of flight information from an in-flight aircraft to either other in-flight aircraft or ground systems. The ADS-B transmission will typically comprise information items such as altitude, flight ID, GPS (Global Positioning System) position, velocity, altitude rate, etc. The transmission medium for ADS-B can implement VHF, 1090 MHz (Mode S), UHF (UAT), VDLM4 or a combination of systems.
The TCAS system was implement by the Federal Aviation Administration (FAA) in the 1980""s to provide aircraft with an on-board collision avoidance system. Since TCAS""s inception it has become a standard for air traffic safety in the United States and abroad. There are two different versions of TCAS, for use on different classes of aircraft. The first, TCAS I, indicates the bearing and relative altitude of all aircraft within a selected range (generally 10 to 20 miles). With color-coded symbols, the Cockpit Display of Traffic Information (CDTI) (i.e., the display) indicates which of the aircraft pose a potential threat. This constitutes the traffic advisory (TA) portion of the system. When pilots receive a TA, they must visually identify the intruding aircraft and may alter their plane""s altitude by up to 300 feet. TCAS I does not offer solutions for avoidance of a potential threat, but does supply pilots with important data so that they can determine the best course of action.
In addition to a traffic display, the more comprehensive TCAS II also provides pilots with resolution advisories (RAs) when needed. The system determines the course of each aircraft and whether it is climbing, descending or flying straight and level. TCAS II then issues an RA advising the pilots to execute the type of evasive maneuver necessary to avoid the other aircraft, such as xe2x80x9cClimbxe2x80x9d or xe2x80x9cDescend.xe2x80x9d If both planes are equipped with TCAS II, then the two computers offer deconflicting RAs. In other words, the pilots do not receive advisories to make maneuvers that would effectively cancel each other out, resulting in a continued threat.
Thus, the collision avoidance logic for TCAS II takes the collected data on the flight patterns of other aircraft and determines whether any of them present a potential collision threat. The overall system does not limit itself to the display of other planes, like a conventional radar screen, but offers warnings and solutions in the form of traffic advisories (TAs) and resolution advisories (RAs).
Traffic alert and Collision Avoidance Systems (TCAS) functionality can be improved with the GPS positioning capabilities of the ADS-B system. Such GPS position information will aid TCAS in determining more precise range and bearing at longer ranges. With greater precision, commercial aircraft can achieve higher safety levels and perform enhanced operational flying concepts such as in-trail climbs/descents, reduced vertical separation, and closely sequenced landings.
Additionally, GPS-based air traffic control systems, such as ADS-B, can also be used to extend traffic surveillance over greater distances. Previous technology limited surveillance ranges to a maximum of about 40 nautical miles (nmn). ADS-B, since it does not require an active TCAS interrogation to determine range and bearing, will not be subject to a power limitation. As a result, in general, the ADS-B receiver capability determines surveillance range. For example, if the ADS-B receiver can process an ADS-B transmission out to 100 nm, then 100 nm is the effective range.
Currently, ADS-B technology is limited in deployment to a select, but constantly growing, number of aircraft while TCAS is a more industry wide standard. As such, the vast majority of current aircraft will rely solely on TCAS intruder data as a means of identifying and avoiding other aircraft within a specified range. Aircraft that are currently equipped with both ADS-B and TCAS technology can benefit from both data streams if the information can be correlated and integrated to provide for more accurate and precise identification of intruders/targets.
Due to variances in accuracy and resolution, the ADS-B and TCAS data for a single intruder aircraft will not be identical. Thus, uncorrelated ADS-B and TCAS data will typically result in two distinct symbols displayed on the CDTI. Therefore, a need exists to provide an on-board correlation method that will allow for a common intruder aircraft to be displayed as a single symbol on a CDTI. Correlation of the data serves to reduce display clutter or confusion that might arise from the display of multiple position symbols for the same intruder/target aircraft.
The present invention provides improved systems and methods for correlating interrogation-based air traffic surveillance, such as Traffic alert and Collision Avoidance System (TCAS) and GPS-based air traffic surveillance, such as Automatic Dependent Surveillance Broadcast (ADS-B). As a result the correlation process minimizes or eliminates the display of two symbols for the same intruder/target on the CDTI of an aircraft. The data correlation and integration process of the present invention allows one unique symbol to be displayed on the CDTI, if the same reporting aircraft is equipped with ADS-B and TCAS broadcast/interrogation capabilities.
Many current aircraft implement interrogation, such as TCAS, as a means of determining intruder aircraft (i.e., aircraft within a specified range), while GPS-based broadcasts, such as ADS-B broadcasts, are somewhat more limited in their current use and availability. As such, the present invention serves to correlate the data in those instances where an aircraft is equipped with both interrogation-based and GPS-based air traffic surveillance capabilities and provide a single icon to a CDTI representing the correlated intruder/target. In instances where aircraft are limited to TCAS interrogation or ADS-B broadcast (i.e. no correlation is needed), the present invention will provide an icon to the CDTI representing an intruder or a target based on the source of data.
In one embodiment of the invention a method for correlating positional data in interrogation-based surveillance and positional data in GPS-based surveillance comprises the steps of receiving a GPS-based broadcast from a target including positional data, correlating the target positional data with positional data from an one or more entries in a interrogation-based intruder file associated with one or more intruders and displaying a single icon on a display terminal if the correlation process results in a determination that the target and one of the intruders are the same aircraft.
In a specific embodiment of the invention a method for correlating TCAS and ADS-S data in an air traffic collision avoidance system comprises the steps of receiving an ADS-B broadcast from an ADS-B target including positional data, correlating the ADS-B positional data with positional data from an one or more entries in a TCAS intruder file associated with one or more TCAS intruders and displaying a single icon on a display terminal if the correlation process results in a determination that the ADS-B target and one of the TCAS intruders are the same aircraft.
Typically, the positional data in the ADS-B broadcast will be used in conjunction with onboard positional data to derive the positional components that will be correlated with the data found in the TCAS intruder file. The TCAS intruder file stores a finite number of entries (typically 30) related to the intruders in proximity to ownship. The correlation method compares the positional data related to the ADS-B target and each TCAS intruder in the file and determines which, if any, ADS-B target and TCAS intruder is the most correlated in terms of position. If the correlation process is successful then the ADS-B target and the TCAS intruder are deemed to be the same aircraft and the cockpit display of traffic information (CDTI) displays one icon on the display terminal representing one aircraft. If the correlation process does not result in the ADS-B target and any TCAS intruder in the file being correlated then the CDTI displays two icons representing two possible aircraft.
In one embodiment of the invention the correlation method comprises the following steps. The method is initiated by determining deltas of predetermined components of the ADB-S positional data and positional data associated with a TCAS intruder file entry. In one embodiment of the invention the predetermined components are defined as range, relative altitude and relative bearing. The deltas are assigned a predetermined progressive weight and they are then summed to ascertain a total confidence score. This process is undertaken for every qualifying ADS-B target and TCAS intruder correlation pair. After all entries in the intruder file have been processed a determination is made as to which pairing has the highest total confidence score. The highest total confidence score is deemed to be correlated (i.e., the same aircraft) and one icon is displayed on the CDTI.
In one embodiment of the present invention the correlation routine may compare one GPS-based broadcast message related to a target to all entries in the interrogation-based entry file, each entry related to an intruder. In an alternate embodiment, the correlation routine may compare multiple GPS-based broadcast messages related to multiple targets to all entries in the interrogation-based entry file.
The invention is also embodied in a system for correlating interrogation-based intruder position data and GPS-bases target position data in an air traffic control system. The system will comprise a means for receiving a GPS-based broadcast associated with a target, the broadcast including positional data. The means for receiving a GPS-based broadcast may include a Mode S transponder, a Universal Access Transceiver (UAT), a VHF Data Link Mode 4 (VDLM4) or any other suitable communication receiver. The system also includes a memory component that stores interrogation-based positional data for one or more intruders. Typically the intruder file will comprise positional data related to a finite number of nearest in proximity intruders. The correlation system includes a processing unit that receives positional data associated with the target from the GPS-based broadcast receiving means and positional data of an intruder from the memory component and implements a routine to determine if the target and the intruder are a single aircraft. The system also implements a display terminal that indicates a single icon if the processing unit determines that the target and the intruder are a single aircraft and two different icons if the processing unit determines that the target and the intruder are individual aircraft.
Through the use of progressive weighting and correlation screening routines the systems and methods of the present invention are able to precisely and accurately correlate GPS-based air traffic surveillance related to targets, such as ADS-B targets and interrogation-based air traffic surveillance related to intruders, such as TCAS intruders. The systems and methods of the present invention are able to overcome variances in accuracy and resolution that result in the ADS-B and TCAS data being incompatible. As such, the present invention is able to correlate the ADS-B and TCAS data such that a single intruder/target aircraft icon is displayed on the CDTI onboard an aircraft, lessening inaccuracies and display confusion on the display terminal.